Note: Descriptions are shown in the official language in which they were submitted.
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
1
OPTICAL BEAM SHAPER
BACKGROUND OF THE INVENTION
The present invention relates to a device for inspecting components and
particularly to one using an array of light sources and video devices as a
means
of evaluating a component for conformance to spatial form criteria.
Presently, there is an ever increasing demand to obtain high quality
products which has resulted in a significant increase in the use of non-
contact
inspection systems. In order for a complex machine to operate as designed, it
is
necessary that all of its sub-components comply with quality criteria. In some
manufacturing settings, customers require 100% inspection of component parts.
For example, fasteners used in the automobile industry and elsewhere often
must
be individually inspected to determine if they meet spatial form criteria.
Numerous types of inspection systems are presently utilized. One type of
system uses contact probes which touch a component at various points to
determine if its dimension or profile meet certain criteria. However, contact
devices have inherent limitations in that they are subject to wear and
generally
require that the component and the contract probe be accurately positioned
during the evaluation process. Moreover, such devices are generally slow to
operate and are limited in terms of the number of criteria and complexity of
profiles which they can evaluate. A variety of non-contact systems are also
known using a variety of techniques. For example, ultrasonic inspection
systems
examine reflected sound waves as a means of characterizing a component.
Various systems based on photodetection utilizing single channel
photodetectors
are also known. In addition, laser gauging systems are used in which specific
dimensional measurements can be obtained.
However, although known non-contact inspection systems are generally
extremely useful, they have certain limitations. Many of the presently
available
non-contact gauging systems require complex data processing approaches which
impose speed limitations in part evaluations. For example, systems utilizing
two-
dimensional photosensitive arrays impose extreme data processing
requirements, which has the effect of reducing part throughput. Preferably,
evaluation of a workpiece can be conducted in a rapid enough fashion that the
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/Z0946
2
parts can be directly sorted into qualified or disqualified part streams. The
systems which are capable of such high speed inspection lack valuable signal
processing capabilities such as edge detection and real time imaging. Edge
detection enhances the accuracy of the inspection enabling the parts
inspection
system to overcome the inherent limitations of discrete photodetectors. Early
photodetection systems and ultrasonic systems provided part shape information
based on the signal strength of a transducer. This information was only an
approximation of the parts shape and not a true image of the part. For example
single channel photodetectors could generate a single output related to the
amount of occluded light. Over a set period of time this single channel
photodetector gives an approximation of the part shape, but not an actual
picture
of the part. There is a need in the art for a high speed inspection system
with
powerful signal processing capabilities which include edge detection and real
time imaging.
SUMMARY OF THE INVENTION
In accordance with the present invention, an improved non-contact
inspection system is provided which enables rapid inspection to be conducted
permitting parts to be immediately sorted in terms of being in conformance or
out
of conformance with spatial form criteria. Moreover, a hard copy of part
geometry
can be generated from a shadow image or occluded light profile of the part
pointing out specific shape discrepancies. For example, for a threaded
fastener,
the diameter, length, profile and threads can be evaluated. When producing
fasteners, the process often begins with wire stock which is fed into a cold
heading or screw type forming machine. The part is die-formed or cut in a
machine into a shape that may include several diameters and possibly a
threaded or knurled length. The formed part may require secondary operations
such as thread rolling, heat treating, planing, etc. It is not uncommon for
one or
more of the processes to fail to produce the desired geometry of part. The
occurrence of such defects is often not adequately monitored through random
part selection or other quality assurance processes which do not provide a
100%
inspection.
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
3
In the present invention parts move by gravity or other means along a
track through a test section. The part shape is determined through use of a
CCD
line array/camera, although any type of photodetector may be used. A
collimated
uniform light source in the form of a sheet is generated in the proximity of
the part
to be inspected. This uniform sheet of light will allow a highly detailed part
examination. The extent and time to which the sheet of light is occluded by
the
part is related to its shape. As the part moves through the test section
containing
the CCD line array, the CCD line array will measure the occluded light and
generate an output signal to a signal processor. The signal processor will
measure the time the part takes to pass over the CCD line array and combine
this time information with the occluded light output signal to generate an
image of
the part. The part measurements of interest are its length and various radial
profiles.
A part detection array utilizes a plurality of light sources and CCD line
arrays in a radial arrangement around the part to be examined. The part
detection array will measure the occluded light from a matched or paired light
source which is proximate to the part. In the preferred embodiment of the
invention a light source is coupled to a diffractive beam shaper which
provides a
uniform sheet of light. The uniform sheet of light is used to attain an even
intensity pattern over a certain area. The shadows created by the parts
because
of the use of the uniform sheet of light are indistinct and lack sharp
transitions to
the lighted areas. In order to interpret these blurred shadow edges special
software detailed below has been created to define the location of the actual
edge. Each light source used in the array will emit only a certain frequency
of
light and each CCD line array will include a filter to allow only its matched
frequency to be detected. In this manner there will be no cross-talk generated
between each light source and its matched CCD line array.
Further objects, features, and advantages of the invention will become
apparent from a consideration of the following description and the appended
claims when taken in connection with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The various advantages of the present invention will become apparent to
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
4
those skilled in the art after reading the following specification and by
reference to
the drawings, in which:
Figure 1 is a perspective view of the non-contact inspection system
according to this invention;
Figure 2 is a view taken along line 2-2 of Figure 1 particularly showing the
test section;
Figure 3 is a diagram of the signal processing system of this invention;
Figure 4 is an elevational view of a representative workpiece;
Figure 5 is a diagrammatic drawing of the light source used in the present
invention; and
Figure 6 is a magnified view of one embodiment of a grating used in the
present invention having an etched surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Figure 1 shows a non-contact inspection system in accordance with the
present invention and is generally shown as 10. Inspection system 10 generally
comprises frame 12, parts sorter bin 14, slide track 16 having test section
18, and
enclosure 20 for housing electronic components of the instrument.
While inspection system 10 can be used for numerous types of
workpieces, an example of one such component is provided in Figure 4 in the
form of a threaded bolt 22 used for mounting the road wheels of a motor
vehicle.
A large number of bolts 22 (referred to as p arts or w o rkpieces ) are
dumped into parts sorter bin 14. Parts sorter bin 14 causes the randomly
oriented
parts 22 to be directed in a desired orientation i.e. headed or threaded end
first,
and causes them to periodically slide down track 16 under the force of
gravity.
As parts 22 pass through test section 18, they are evaluated as will be
described
in more detail in the following portions of this specification. Part 22 is
inspected
for conformance with predetermined spatial form criteria. If a particular part
meets the criteria, it passes into parts bin 24 provided for qualified or go o
d
parts. If, however, the part is deemed to be out of conformance, gate 26 is
actuated and the part is diverted into parts bin 28 provided for disqualified
or
b ad parts. Presumably, good parts will outnumber bad parts and the parts
bins are sized accordingly.
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
Within enclosure 20 is housed computer 32 provided for evaluating the
outputs of the system, controlling the system, and providing a means of
storing
data related to part criteria and inspection history. A pair of displays 34
and 36 is
provided, one of which may output in graphical from configuration data for a
5 particular part, whereas the other may be used for outputting statistical or
other
numerical data related to inspection. In one embodiment of this invention,
displays 34 and 36 were electroluminescent types having touch screens for
interaction with the user. Enclosure 20 has access doors 38 which can be
closed
when the system is not in use.
Details of the elements and operations of test section 18 will be described
with reference to Figures 1 and 2. Within test section 18, evaluations of part
22
profiles are provided. The length of the part 22 (i.e. its dimensions along
its
direction of travel) and various radial profiles (i.e. its form perpendicular
to its
direction of travel) are evaluated by a plurality of profile detection arrays.
The profile detection arrays include light sources 40 and CCD line arrays
or line scan cameras 42, as shown in Figure 2, although any type of
photodetector may be used. The light sources 40 provides a uniform sheet of
light 44 which the part 22 occludes as it travels through test section 18. The
extent and time to which this uniform sheet 44 is occluded by the part 22 is
related to its shape. As the part 22 moves through the test section the CCD
line
arrays 42 will measure the occluded light and generate an output signal and
direct that output signal to a signal processor.
Referring to Figure 5, the preferred embodiment of the light source 40 is
detailed. A framework 46 supports and encloses control and power circuitry
including a laser control board 48 and a glass board 50 for the light source
40. A
laser diode 52 has a power intensity which is controlled by the laser control
board
48 which may be further connected to an external control system by a data
communication link so that it may be integrated into a manufacturing line.
Although a laser diode 52 is shown, any other type of light or laser light
generator such as alternate semiconductor lasers, gas lasers, solid state
lasers,
and liquid dye lasers may be used with the present invention.
The laser diode 52 generates laser light 54 which is incident upon a
diffractive beam shaper 56 that maps an input intensity distribution to an
output
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
6
intensity distribution. The diffractive beam shaper 56 may include gratings,
prisms, grisms, lenses, and interferometers to create the desired fringe
patterns
and intensity distributions. The fringe patterns will vary in width and
orientation,
depending on the diffractive beam shaper's 56 characteristics. By designing
the
diffractive beam shaper 56 with an appropriate fringe pattern, one can reflect
light
into different directions based on the equations describing the different
characteristics of the diffractive beam shaper 56.
Figure 6 illustrates one embodiment of the diffractive beam shaper 56 of
the present invention as an etched glass grating 70. The surface of the glass
grating 70 has been magnified to show the etched 72 and nonetched 74 regions.
The etched regions 72 are represented as darker areas and the nonetched
regions 74 are represented as lighter areas. The grating 70 operates as
follows:
rays of light are deflected at larger angles where the nonetched 74 regions
are
narrower and close together, and are deflected by smaller angles where the
nonetched regions 74 are wider and farther apart. In this way the incident
light
can be evenly distributed as it exits the grating 70. The etched 72 and
nonetched
74 regions have dimensions with magnitudes corresponding to the chosen light
wavelengths incident upon the grating 70. For example, the width of one of the
nonetched regions 74 may be one wavelength.
One application of the diffractive beam shaper 56 of the present invention,
is to take a Gaussian input (i.e. a Gaussian intensity distribution on the
aperture
of a beam shaper) and map that to a "top hat" distribution (an ideal top hat
intensity distribution has only one intensity value inside a certain radius
and zero
intensity value outside that radius). The function can be thought of as a
general
ray deflection function. The most intense light at the center of the Gaussian
input
is deflected radially outward, while the light in the tail of the Gaussian is
deflected
slightly inward. In this way the intensity of the output beam can be tailored.
After exiting the diffractive beam shaper 56, the laser light 54 is further
conditioned by a refractive spherical or cylindrical lens 58. The lens 58
reduces
the divergence of the laser light 54 and therefor reduces the need to
manufacture
more precise diffraction devices in the diffractive beam shaper 56.
Additionally, a
conventional refractive element might also be used to roughly collimate the
output beam. The laser light 54 will finally be conditioned by a convex lens
60 in
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
7
order to focus the laser light 54. The output of the light source 40 will then
comprise a uniform sheet of light 44. By combining diffractive beam shapers
and
conventional refractive devices, one can produce a family of intensity
distributions such as a line that varies as a Gaussian distribution across its
width
but has a uniform intensity along its length. Furthermore, while the
diffractive
beam shaper 56 of the present invention is depicted for use with a parts
inspection system, it may be used in any other application in which a coherent
collimated light source having a uniform intensity distribution may be used.
As discussed previously in the operation of the inspection system 10, a
part 22 will occlude a portion of the light rays and create a shadow against
the
CCD line arrays 42. The shadows created by the parts are indistinct and lack
sharp transitions to the lighted areas. In order to interpret these blurred
shadow
edges special software has been created to define where the actual part edge
is
on the CCD line arrays 42. Each light source 40 used in the array will emit
only a
certain frequency of light and each CCD line array 42 will include a filter to
allow
only its matched frequency to be detected. In this manner, there will be no
cross-
talk generated between each light source and its matched CCD line array 42.
A CCD line array is an electronic imaging device which contains a linear
row of discrete photo sensing elements or pixels which convert incident light
into
an electrical signal. The strength of the signal is directly related to the
intensity of
light striking the pixels. The CCD line array generates an output signal
composed of a plurality of digital and analog signals. Each pixel when
saturated
by an intense light can function as an o n condition or when fully blocked can
function as an off condition. There are also circumstances when certain
pixels may be only partially blocked. During these periods, the pixels can
generate analog signals proportional to the amount of light they are
receiving.
The CCD line array converts the incident light on each pixel into discrete
charge
packets. The amount of charge generated or integrated onto each pixel is a
function of the integration time, and the intensity and wavelength of the
light
focused on the photocell. After an appropriate integration period, the charge
packets are transferred simultaneously into high speed CCD shift registers 62
for
transport to a signal processor 64 as shown in Figure 3.
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
8
CCD line arrays can operate with data ranges in the megahertz or more
and produce 70,000 or more scans per second. The data is also available
immediately whereas a particular line from an area sensor is only available
after
the lines preceding it have been read out. Furthermore, the lines are
sequential
and are available one right after another. This makes CCD line arrays ideally
suited for applications where motion is present. Typically in the present
invention, a CCD line array is placed so as to align the row of pixels
perpendicular to the direction of motion. That makes resolution in the
direction of
motion dependent on integration time, pixel size and the motion velocity. In
the
present invention the CCD line array can be adjusted to suit the application.
The CCD line array possesses excellent uniformity. Since a line scan
camera contains a single row of pixels, the uniformity can be held much
tighter
than in an area array with several hundred thousand pixels. In the present
invention high precision imaging applications, contrast correction hardware,
and
software algorithms are more easily implemented over a single line of pixels.
Another valuable property of the CCD line array is that an infinitely long or
continuous picture can be generated. In effect, that is what a continuously
moving conveyor belt or other continuous feed system presents to the camera.
The CCD line array will not chop off images as an area camera would need to in
order to examine data. The CCD line array is a practical solution for the high-
speed imaging of continuous feed systems.
Once the CCD line array has sampled the image it must transfer its output
signals to an image processor. As seen in Figure 3, in one embodiment of the
present invention, a microcomputer such as a PC is equipped with a signal
processor-I/O card 64 and interface to the CCD line arrays 42. The present
invention is preferably integrated with an Intel based PC although other
computers including Sun workstations, Hewlett Packard workstations, Silicon
Graphics workstations, Macintosh computers, IBM workstations, Motorola
microprocessor based PC s, and digital controllers may be used. The output
from the CCD line arrays 42 is composed of sequential contiguous lines. These
lines are processed in the order in which they are received. The shift
registers 62
transfer discrete and analog information to the signal processor-I/O card 64
located in a computer 32. The signal processor 64 will interpret analog and
CA 02379561 2002-O1-31
WO 01/09665 PCT/US00/20946
9
digital information transferred by the shift registers 62, the signal
processor 64
will in effect, rearrange the lines into the correct sequence. The processed
data
will then be stored in memory 66 to be further manipulated by microprocessor
68.
In the preferred embodiment of the present invention proprietary software
has been constructed to aid in the detection of workpiece edges being examined
by the inspection system. This software is designed to interpret the blurred
shadows cast by the part onto the CCD line arrays 42 as it occludes the light
from
the diffuse light source. The pixels of the CCD line arrays 42, as discussed
previously, have the ability to generate analog signals proportional to the
amount
of light they are receiving. The pixel signals generated by the pixels
receiving the
blurred shadow edges will generate signals representing a light strength
gradient
from those pixels completely occluded to those completely unoccluded. The
software will interpret this gradient and predict where the edge of the part
should
be.
It is to be understood that the invention is not limited to the exact
construction illustrated and described above, but that various changes and
modifications may be made without departing from the spirit and scope of the
invention as defined in the following claims.
